ATLAS

Abstract:

A search for new particles that decay into top quark pairs (ttbar) is performed with the ATLAS experiment at the LHC using an integrated luminosity of 4.7 fb^-1 of proton-proton (pp) collision data collected at a center-of-mass energy sqrt(s)=7 TeV. In the ttbar --> WbWb decay, the lepton plus jets final state is used, where one W boson decays leptonically and the other hadronically. The ttbar system is reconstructed using both small-radius and large-radius jets, the latter being supplemented by a jet substructure analysis. A search for local excesses in the number of data events compared to the Standard Model expectation in the ttbar invariant mass spectrum is performed. No evidence for a ttbar resonance is found and 95% credibility-level limits on the production rate are determined for massive states predicted in two benchmark models. The upper limits on the cross section times branching ratio of a narrow Z' resonance range from 5.1 pb for a boson mass of 0.5 TeV to 0.03 pb for a mass of 3 TeV. A narrow leptophobic topcolor Z' resonance with a mass below 1.74 TeV is excluded. Limits are also derived for a broad color-octet resonance with Gamma/m = 15.3%. A Kaluza-Klein excitation of the gluon in a Randall-Sundrum model is excluded for masses below 2.07 TeV.

Abstract:

We outline the experimental concept and key scientific capabilities of AION (Atom Interferometer Observatory and Network), a proposed UK-based experimental programme using cold strontium atoms to search for ultra-light dark matter, to explore gravitational waves in the mid-frequency range between the peak sensitivities of the LISA and LIGO/Virgo/ KAGRA/INDIGO/Einstein Telescope/Cosmic Explorer experiments, and to probe other frontiers in fundamental physics. AION would complement other planned searches for dark matter, as well as probe mergers involving intermediate mass black holes and explore early universe cosmology. AION would share many technical features with the MAGIS experimental programme in the US, and synergies would flow from operating AION in a network with this experiment, as well as with other atom interferometer experiments such as MIGA, ZAIGA and ELGAR. Operating AION in a network with other gravitational wave detectors such as LIGO, Virgo and LISA would also offer many synergies.

Abstract:

We have carried out a series of magnetic field measurements using a portable three-axis SQUID magnetometer at the Laboratoire Souterrain à Bas Bruit (LSBB), Rustrel, France. The magnetometer was originally developed as part of the cryoEDM neutron electric dipole moment experiment [1], where we need to monitor drifts in the magnetic field at a level of ∼0.1 pT. The cryoEDM SQUID system is a 12-channel magnetometer designed to operate in a large cryostat with extensive magnetic shielding [3]. We have tested smaller prototype systems during a series of trips to LSBB [2], primarily to test the SQUIDs, and control and DAQ electronics in a low noise environment. However this investigation also provided an opportunity to characterise the magnetic environment at different locations within the LSBB complex. We monitored the magnetic field at various positions inside the underground laboratory, including the Capsule, the Galerie Anti-Souffe (GAS) and the Galerie Gaz-Brûlés (GGB). We recorded several hours of data at each location to compare with that recorded at the same time by the LSBB [SQUID]2 system permanently installed in the Capsule, and from this we have characterised the relative amplitudes of magnetic field fluctuations in the different locations. SQUID resets are corrected using software, but as this process is not perfect an accurate comparison can only be done during stable periods. Software development and data analysis are still in progress. Preliminary analysis suggests the magnetic field measured in the Capsule is approximately 75% that measured in the GAS and GGB.